Agree with Shade. Prongs, if used properly, are not even remotely cruel and are much safer and more effective than choke chains. They're a tool, and shouldn't necessarily be a permanent solution. I have a 7 month old female who is VERY strong, and I used a prong for a couple of weeks to aid with training (rather than as a crutch) and now no longer need to.
Delta zur Bindenburg- 11/15/13
Gentle Tripp- 6 yr old OTTB mare